My biggest advice would be to try and lock one of his arms. It restricts movement and can still be kept in the move to avoid struggling.
Get a body triangle-like guard at your opponents hips. Keep your knees in tight to his hips, this should make it harder to break guard.
Try to trap one arm at the bicep under your armpit. Grab his head with your other and press it under your other armpit. Try to have near the back of his neck at your armpit.
Gable-grip both hands together firmly. The gable grip makes it harder to break with his remaining hand.
Next, move your body triangle as high as you can go. Hold your legs tight. Now try to get your legs and necks as far away apart as possible.
I tried to break this down as simply as I could. Honestly, your club should be teaching you this.
"Thank God For One More Day" - Wanderlei Silva